This invention relates to the use of various nonionic and cationic surfactants during the preparation of 2,2'-dithiobis (benzothiazole) to reduce or eliminate the formation of large particles in the product.
The production of 2-mercaptobenzothiazole (a starting material for the production of 2,2'-dithiobis (benzothiazole)) from aniline, carbon disulfide and sulfur, as described by Kelly in U.S. Pat. No. 1,631,871, is accompanied by the production of unwanted tarry by-products. As part of the purification process, the crude mercaptobenzothiazole is dissolved in caustic solution, thereby effecting formation of the sodium salt of mercaptobenzothiazole. However, many of these by-products pass into the aqueous caustic solution either as salts or as dissolved impurities. During the chlorine/air oxidation of this solution to form 2,2'-dithiobis(benzothiazole), tarry droplets and large agglomerates form as a result of the presence of these impurities, along with the desired product. These particles and agglomerates are known in the art as "sand" and are fairly large in size in relation to the particles of the reaction product. The presence of this "sand" causes problems when the benzothiazole is compounded into rubber stock as a vulcanization accelerator. Physical removal of some of these particles is possible by sieving but this requires extra processing steps and significant amounts of 2,2'-dithiobis(benzothiazole) contained in the "sand" are removed and subsequently must be recycled in some manner.
Therefore, a process in which 2,2'-dithiobis (benzothiazole) is produced with uniform particle size is desirable.
U.S Pat. No. 2,830,058 discloses that sand formation is reduced or eliminated if anionic surfactants, like sodium stearate, are present at concentrations of 1 to 15% during the oxidation of mercaptobenzothiazole to benzothiazolyl disulfide. Furthermore, the patent asserts that nonionic and cationic surfactants appear to be substantially inactive for this purpose.